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# 用比例解决问题 - PowerPoint PPT Presentation

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12.8÷8=1.6(元)

10吨水多少元?

1.6×10=16(元)

10

12.8

8

=

12.8×10

8

X =

8X = 12.8×10

X = 16

12.8÷8=1.6(元)

19.2元可以用多少吨水?

19.2÷1.6=12(吨)

X

12.8

8

=

19.2×8

12.8

X =

12.8X = 19.2×8

X = 12

30

X =

30X = 20×18

X = 12

15

X =

15X = 20×18

X = 24

（1）设要求的问题为x；

（2）用正比例或反比例的意义判断题中的两种量成正比例还是成反比例关系；

（3）列比例式；

（4）解比例，验算，作答。

1、比例尺一定时，图上距离和实际距离成正比例.（ ）

×

2、圆的周长公式中当C一定时,π与d成反比例.（ ）

×

3、速度与路程成正比例。（ ）

4、y︰8＝x（x不是0），y和x成正比例。（ ）

500用比例解这类问题的过程可以归纳为以下几个步骤：千克的海水中含盐25千克，120吨的海水含盐几吨？